Flexible detonating compositions containing high explosives and polymeric metallocarboxylates



g- 29, 1967 w. L. EVANS 3,338,764-

FLEXIBLE DE'I'ONATING COMPOSITIONS CONTAINING HIGH EXPLOSIVES ANDPOLYMERIC METALLOCARBOXYLATE Filed Aug. 19. 1965 INVENTOR WILLIAM L.EVANS ATTORNEY United States Patent 3,338,764 FLEXIBLE DETONATINGCOMPOSITIONS CON- TAINING HIGH EXPLOSIVES AND POLYMERICMETALLOCARBOXYLATES William L. Evans, Blackwood, N.J., assignor to E. I.du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware Filed Aug. 19, 1965, Ser. No. 481,150 21 Claims. (Cl. 14919)This invention relates to novel explosive compositions, to flexible,shaped, detonating articles made from said compositions, and to methodsfor manufacturing such nating fuse known under the name Cordeau (US.

Patent No. 869,219) which consisted of a metal tube, generally of leador lead alloy, filled with tn'nitrotoluene. This fuse, however, wasrelatively low in tensile strength, especially in small diameters; waseasily deformed or fractured by mild impacts and by bends because of itslow order of resilience, toughness and tensile strength; .was relativelyheavy per unit of length; was relatively low in initiating power becauseof the metal sheath surrounding the explosive core; could not be usedabove about 175 F. because the explosive core melted and became lesssensitive; and was expensive to manufacture.

An effective successor to Cordeau is a detonating fuse which consists of:an explosive core of PETN (pentaerythritol tetranitrate) containedwithin a waterproofed textile covering or a textile and plasticcovering, these assemblies for a given length of detonating fuse beingonly about one-fifth as heavy as the same length of Cordeau.Commercially available forms of this detonating fuse are well known.They have much greater tensile strength than Cordeau fuse, betterresistance to deformation, are relatively easy to handle and use, andhave a higher velocity of detonation and better priming power. At aconsiderable increase in cost, detonating fuse having even highertensile strength can be obtained by applying metal wire wrapping overthe fabric covering. The flexibility of the fabric-covered cord,however, is inadequate for satisfactory use at temperatures below about40 F., and the flexibility is even further impaired by the presence ofreinforcing wire coverings. Although PETN, the explosive core, is notsoluble in water and absorbs water very slowly, the above describedfabric-covered, PETN-containing, detonating fuse is not completelyWaterproof; for example, wet ends may lead to priming failures, andfailure of propagation of detonation to branch lines may occur if waterpenetrates at knotted connections Where the waterproofing cover isbroken. Furthermore, knotted connections may cause failures ofpropagation unless the branch line is at an angle greater than about 30from the main line in the direction of detonation.

Flexible detonating compositions, as well as shaped articles containingsuch compositions, also have become available in recent years in theform of sheets, cords, and

other shaped masses as disclosed in US. Patent Nos. 2,992,087,2,999,743, 2,965,466, 2,999,744, 3,018,201, and 3,116,186. Thesedetonating compositions generally comprise a cap-sensitive explosiveheld in a matrix of one of several polymeric binders, incorporation ofwhich requires exothermic fluid polymerization, relatively hightemperature curing, or incorporation in volatile, toxic or flammablesolvents which subsequently are removed; all

' processes which are unattractive from the standpoint of safety inmanufacture, and generally give products which lack flexibility at lowor subzero temperatures, or have limited toughness at ordinarytemperatures, said toughness being further reduced at elevatedtemperature. These deficiencies in physical properties are especiallyapparent, for example, in the ease with which the compositions are cutthrough by reinforcing members under tension, in the significant loss oftensile strength as temperatures of the compositions increase from roomtemperature to 140 F. or even higher, and in the brittleness which isapparent at temperatures of 0 F. and lower. The manufacturing proceduresemployed and some of the binders used in the explosive compositions areinherently expensive to the point of resulting in flexible productswhose limited special properties are attained only at a considerableeconomic penalty.

The potential utility of shaped explosive articles comprisingparticulate cap-sensitive detonating explosives in a natural orsynthetic rubber matrix was disclosed in US. Patent 2,067,213, andmethods of manufacturing the compositions by incorporating thecap-sensitive high explosives in water-bearing rubber latices also weredisclosed. Such compositions and the articles made from them, however,were not suitable for general use over the wide range of temperaturesencountered under normal conditions of use in the explosive industrybecause the articles lost their flexibility and became stiff and brittleat relatively low temperatures, of the order of 0 F., and lackedsufiicient tensile strength for satisfactory use at the higher end ofthe temperature range, e.g., about 120 F. As a result, detonating tapes,sheets, cords and trains made from such compositions were not generallyadopted for use in the industry.

An object of this invention is to provide novel explosive compositions.A further object of the invention is to provide explosive compositionsthat are flexible. Another object of the invention is to provide a noveldetonating fuse that has superior properties of flexibility and tensilestrength over a wide temperature range. Another object of the inventionis to provide a commercially feasible and economical method for makingexplosive compositions and also for fabricating the compositions intovarious shapes for subsequent use.

It has now been discovered that novel explosive compositions areobtained by intimately mixing a polymeric carboxylic elastomer that is acopolymer of from about 50 to percent by weight of a butadiene, fromabout 10 to 45 percent by weight of an acrylonitrile and a sufficientamount of an acrylic acid to provide from about 0.001 to 0.3 carboxylequivalents per parts by weight of said copolymer; a source ofpolyvalent metal ions in an amount chemically equivalent to about 0.5 to2 times the carboxyl content of the copolymer; from about 1 to 20percent by Weight of a plasticizer; and

from about 40 to 80' percent by weight of a particulate cap-sensitivehigh explosive. Preferably, but optionally, up to 25 percent by weightof a liquid polyurethane elastomer is added to the explosive compositionin order to obtain optimum physical properties in relation toflexibility.

Thus, the novel elastomer-bonded explosive composition of the presentinvention comprises an intimate uniform mixture of from about 40 to 80percent by weight of a cap-sensitive particulate high explosive, fromabout 15 to 50 percent by weight of a polymeric metallocarboxylateelastomer and from about 1 to 20 percent by weight of a plasticizer forthe carboxylate elastomer. The polymeric metallocarboxylate elastomer isthe reaction product of a polyvalent metal ion, which acts as a curingagent for the elastomer, with a copolymer of from about 50 to 80 percentby weight of a butadiene, from about to 45 percent by weight of anacrylonitrile and a suflicient amount of an acrylic acid to provide fromabout 0.001 to'0.3 carboxyl equivalents per 100 parts of said copolymer,the polyvalent metal ion being present in an amount chemicallyequivalent to about 0.5 to 2 times the carboxyl content of saidcopolymer. Most preferably, the explosive composition contains up toabout 25 percent by weight of a polyurethane elastomer. However, theamount of polyurethane, if used, should generally not exceed about theamount of metallocarboxylate elastomer.

The resultant explosive composition is flexible and can be formed into avariety of shapes that retain substantially the dimensions and form intowhich the compositions are fabricated. For example, the explosivecompositions can be shaped by pressing into blocks, slabs or sheets, byrolling into sheets and films, and by extruding into rods, cords, tubesor sheets. The shaped articles are flexible, yet have a desirable hightensile strength. These explosive compositions have been found to beparticular ly useful and supply a long sought after need in theexplosive industry, especially when formed into tubes, tapes and cordswhich can be produced by, for example, continuous rolling or extrusionoperations. It has been found that explosive cord, or as it is morecommonly referred to in the industry, detonating fuse, fabricated fromthe novel explosive compositions, and preferably, but not necessarily,containing a reinforcing element and a polyurethane elastomer, greatlyincreases the uses and conditions under which detonating fuse operatesefiectively. For example, flexibility and strength of the detonatingfuse of this invention are retained to such an extent that thecompositions and articles of the invention are useful over a temperaturerange of from about 50 F. to 180 F.

In relation to detonating fuse, any reinforcing element that iscompatible with the explosive composition can be used. Optimum physicalproperties as to flexibility and tensile strength are obtained when theexplosive composition is formed into an elongated or cord-shaped fuse,and yarn, particularly nylon yarn, is employed as the reinforcingelement which is substantially centrally positioned within the fuse andalong its longitudinal axis.

In order to more fully describe a preferred embodiment of a detonatingfuse and its method of preparation, reference is made to the singlefigure in the drawing illustrating one means for manufacturingdetonating fuse.

The drawing illustrates a cross sectional view of an apparatus forextruding the explosive composition around a central reinforcing memberin order to make a reinforced detonating fuse, which is a preferredembodiment of the invention. The apparatus comprises a ram type extruder10 and a barrel 12, a ram 11 at one end of extruder 10 and a formingmeans comprising a die 15 at the.

through guide insert 14 into the explosive composition. In operation,when pressure is applied to the ram 11, provided with 0 type sealingrings 16, it thus forces the explosive composition through die 15 whilethe reinforcing element is simultaneously fed through guide 13 and guideinsert 14 at a predetermined synchronized rate into the explosivecomposition thus forming detonating fuse 19. The detonating fuse may bewound on a spool, or other suitable means, for storage.

After the detonating fuse has been formed, e.g., extruded, it is cured.Curing is merely the completion of the reaction between the polyvalentmetal ion and the carboxylic elastomer and can take place at roomtemperature during storage. However, heating the detonating fuse attemperatures below the decomposition temperature of the particulatecap-sensitive high explosive greatly reduces the curing time. Aconvenient curing temperature being of the order of 160 to 225 F. andfrom about 8 to 24 hours.

High explosives suitable for use in the present'invention includeparticulate cap-sensitive materials which are stable under theprocessing conditions, which are compatible with other ingredients ofthe compositions, and which are not dissolved by other components of themixtures. The cap-sensitive particulate high explosive constitutes 40 topercent by weight of the explosive composition. Representativecap-sensitive high explosives that can be used are trinitrotoluene(TNT), pentaerythritol tetranitrate (PETN), trinitrophenylmethylnitramine (tetryl), cyclotrimethylenetrinitramine (RDX),cyclotetramethylenetetranitramine (HMX), mannitol hexanitrate,tetranitrodibenzo-l,3a,4,6a-tetraasapentalene, di azidodinitrophenol,hexamethylene triperoxydiamine, picrylsulfone, potassiumdinitroacetonitrile, and lead azide. PETN, tetryl, and RDX are thepreferred cap-sensitive explosives of the composition, and especiallypreferred for general use is PETN. The particle size of the highexplosive is not critical to the success of the invention, althoughparticles all of which pass an 80-mesh U.S. standard sieve arepreferred, and especially preferred are particles whose major dimensionson the average does not exceed microns. The latter are designated hereinas superfine explosives. Generally, the compositions are more sensitiveto initiation if they contain a very fine crystalline cap-sensitiveexplosive. The particulate, cap-sensitive high explosive may be dry whenadded for incorporation into the mixture or it may be wet with water,since Water is a major component in the latex of the reaction mixture.Use of water-wet high explosive adds to safety in the manufacturingoperation since the water acts as a desensitizer until the explosive isthoroughly incorporated with the carboxylic elastomer and plasticizer,after which the water is removed, for example, by heat and vacuum.

Any plasticizer for the carboxylic copolymer of the explosivecomposition can be used. Incorporating from about 1 to 20 percentplasticizer by weight assists in providing low temperature flexibilityfor the explosive composition. Plasticizers which are particularlysuitable for use either alone or in combination in said compositions areesters and include, for example, triethyleneglycol-di-Z-ethylhexoate,di-n-butyl phthalate, tricresyl phosphate, acetyl tributyl citrate,isodecyloctylphthalate, di-isodecyl adipate, di-isooctyl adipate,dioctyl adipate, dioctyl sebacate. Particularly preferred plasticizersare din-butyl phthalate and triethyleneglycol di-Z-ethylhexoate whichmay be used either alone or in combination. Other plasticizers which maybe used include, for example, di- (butoxyethoxyethyl)formal, tris([3chloroethyl) phosphate, and highly aromatic oils such as Mobilsol N,Picco 25, and Dutrex 1739. Preferably these will be used in combinationwith one of the organic ester type plasticizers named above.

Carboxylic elastomers which are suitable for manufacture of compositionsand articles of this invention and constitute the major portion of thebinding matrix thereof are copolymers formed from abutadiene-1,3-hydrocarbon, an acrylic nitrile, and an acrylic acid.Typical butadiene- 1-3-hydrocarbons used in preparing said copolymersare, for example, butadiene-1,3 and the 5 to 9 carbon atom homologuesthereof such as isoprene, 2,3-dimethylbutadiene-1,3,pentanediene-1,3,hexadiene 1,3 and mixtures thereof. Asused herein, the term acrylic nitrile refers to acrylonitrile andalpha-substituted acrylonitriles, that is, compounds having the formula:

Examples of acrylic nitriles are acrylonitrile, methacrylonite,ethacrylonitrile, alpha-butylacrylonitrile, alphaphenyl acrylonitrile,alpha-chloroacrylonitrile and alphamethoxymethyl acrylonitrile andmixtures thereof.

Carboxyl groups are introduced into the copolymers by copolymerizing theaforementioned butadiene-1,3-hydrocarbons and acrylic nitn'les with atleast one acrylic acid. Copolymers containing about from 0.001 to 0.3,and preferably 0.02 to 0.15, carboxyl equivalent of at least one acrylicacid per 100 parts by weight of copolymer are preferred. As used hereinthe term carboxyl equivalent of an acrylic acid refers to the amount ofthe chemically combined acrylic acid which contains one equivalentweight, that is, 45 parts .by weight of free carboxyl groups. The amountof free carboxyl groups in a given copolymer can be determined bytitrating a solution of the carboxylic-modified copolymer with alcoholicpotassium hydroxide to a phenolphthalein end-point. As used herein, theterm acrylic acid refers to acrylic acid and alphasubstituted acrylicacids, that is, compounds having the structural formula:

1 CHFC-C 0 OH Acrylic acids which are copolymerized with butadiene-1,3-hydrocarbons and acrylic nitriles thereby introducing free carboxylgroups into the copolymers are, for example, acrylic acid, methacrylicacid, ethacrylic acid and alpha-chloro acrylic acid. Copolymers of from50 to 80% by weight of a butadiene and from about 10 to 45% by weight ofan acrylonitrile containing from about 0.001 to 0.3, and especially 0.02to 0.15, carboxyl equivalent of an acrylic acid per 100 parts -by weightof copolymer are preferred. Especially preferred carboxylic copolymersfor use in making articles of the present invention are made frombutadiene-1,3, acrylonitrile, and methacrylic acid.

Although said copolymers may be incorporated into the explosivecomposition by first dispersing them in volatile organic solvents suchas aliphatic hydrocarbons, halogenated aliphatic hydrocarbons, toluene,or methyl ethyl ketone, the preferred form of the copolymers is a latexcontaining from about 35-60% of solids dispersed in an aqueous medium.Such latices present several advantages since latices are the form inwhich said copolymers are made and, therefore, represent the lowest costform of the copolymers; no costly and hazardous organic solvents arerequired to fabricate the articles of this invention; and finally thepresence of water in the latex greatly increases the safety of mixingoperations wherein a cap- -sensitive particulate high explosive isincorporated with the copolymer, the plasticizer, and the source ofpolyvalent metallic ion. During mixing the reaction mixture may beheated to slowly remove the water or solvent.

7 Several grades of said butadiene-1,3, acrylonitrile, methacrylic acidcopolymers may be made, depending upon the ratios of the monomericmolecules whichare incorporated in the copolymer. Generally these aredescribed as high, medium, or low acrylonitrile copolymers depending onthe proportion of acrylonitrile incorporated in the copolymer, e.g.,50-35%, 35-17%, and 17-1%, respectively for high, medium, and low; andare further characterized by the carboxyl content of the copolymer, asindicated above. For manufacture of articles of the present invention,latices of copolymers of intermediate acrylonitrile content, andcarboxyl (COOH) content of 0.02 to 0.15 parts by weight per 100 parts ofcopolymer, are preferred. Such latices are commercially available as,for example, Hycar 1570X20, 1570X36, 1571 and 1572 (made by the B. F.Goodrich Chemical Co.), of which Hycar 1572 is especially suitable. Suchcommercially available copolymer latices may be used alone, or in combination with one another or in combination with polyurethane elastomersin order to obtain the physical properties desired in the finishedcompositions. Adjustments of compositions, curing agents and processingconditions to obtain desired physical properties is well known inelastomer technology and is regularly practiced by those familiar withelastomer art.

Any source of polyvalent metal ions can be used as a curing agent forthe carboxylic copolymer. Polyvalent metal oxides, hydroxides and othersources of polyvalent metal ions such as salts of an acid weaker thanacetic acid, and salts of an acid readily eliminated from thecrosslinking site, and even finely divided metals, are compounded with,and are used to cure, said carboxylic copolymers hy formingcorresponding metallocarboxylate. Representative examples of such metaloxides and other sources of polyvalent metal ions are, for example, zincoxide, calcium oxide, magnesium oxide, difbutyltin oxide, lead oxide,barium oxide, cobalt oxide, tin oxide, zinc carbonate, calcium silicate,zinc acetate, sodium aluminate, sodium phosphomolybdate, and mixturesthereof. Zinc oxide is preferred. Usually from about 0.5 to 2 times thechemical equivalent weight of polyvalent metallic oxide, or other sourceof polyvalent metal ion, with respect to the amount of carboxyl group insaid carboxylic copolymer is used in formulating compositions andarticles of this invention.

It can be seen from the above that the metallocarboxylate is thereaction product, formed in situ, between a polyvalent metal ion and acarboxylic copolymer of a butadiene, an acrylonitrile, and an acrylicacid, said copolymer containing from 0.001 to 0.3 carboxyl equivalentsof an acrylic acid for each parts by weight of copolymer, andconstitutes 15 to 50% by weight of the explosive composition. At leastabout 15% of the polymeric metallocarboxylateis required to give thedesired flexibility, abrasion resistance, and tensile strength to thecompositions, but if more than about 50% of said metallocarboxylate ispresent, the sensitivity of the explosive composition may be less thanis desired for effective initiation and propagation of detonation,especially in articles of small cross section or diameter, or acrossjoints between articles. The carboxylic copolymers which are used in thecompositions, and their methods of preparation are described in detail,for example, in U.S. Patent Nos. 2,395,017 and 2,724,707 and are furtherdescribed in A New High-Strength Elastomer, Rubber World, 130, 784-8(1954); Carboxylic Elastomers, Industrial and Engineering Chemistry, 47,1006-12 (1955); and Rubber Chemistry and Technology, 28, 937 (1955).

Preferably, up to about 25 percent by weight of a polyurethaneelastomer, either a polyether or linear polyester type, is incorporatedin the explosive composition. The addition of a polyurethane elastomeris especially desirable in explosive compositions which are to be shapedinto detonating fuse. Liquid polyurethane elastomers which arecharacterized by having reactive isocyanate groups by which said liquidpolymers can be cured to form solid elastomers, as is well known in theart pertaining to synthetic elastomers, are particularly suitable andare commercially available as, for example, Adiprenes L-l00, L-l67,L-315, and L-420 which are manufactured by E. I. du Pont de Nemours &Co.

Adiprene L-100 is a liquid polyether urethane elastomer which is made byreacting 1 mol of polytetramethylene ether glycol (PTMEG) of numberaverage molecular weight about 1000 with about 1.6 mols of mixedtolylene diisocyanates, as disclosed, for example, in US. Patent Nos.2,929,800 or 2,948,691. Adiprene L-315 also is a liquid polyetherurethane elastomer and is made by reacting 1 mol of PTMEG of numberaverage molecular weight about 1000, 1 mol of butanediol-1,3 and about 4mols of mixed tolylene diisocyanate isomers for 4 hours at 80 C. undernitrogen, as disclosed in US. Patent No. 3,188,302. Such liquidpolyether urethane elastomers sometimes are designated as prepolymers orintermediate polymers because on reaction with cur1ng agents they arecured or vulcanized to form solid elastomers.

Liquid polyurethane elastomers, even when incorporated into compositionsof the invention without added curing agents, do cure to some extent andenhance the toughness of the final explosive composition. Preferably,however, curing agents for the liquid polyurethane elastomers also areincluded in the formulation, as exemplified hereinafter. Said curingagents include diamines, polyols, titanate esters, and others well knownin the art. Diamines are the best general purpose curing agents, and4,4'-methylenebis(2-chloroaniline), commonly designated MOCA, ispreferred. By reaction with said diamine, for example, the liquidpolyurethane elastomer is converted to a cured solid polyurethaneelastomer which forms a part of the rubbery binder matrix of theexplosive compositions and articles of the invention.

The designated carboxylic elastomers and polyurethane elastomers areespecially suitable for the preparation of shaped articles, e.g.,detonating fuse, of the present invention because these polymers can becrosslinked, i.e., vulcanized or cured, at temperatures much lower thanthose employed with other elastomers. Curing may be achieved even atroom temperature, but preferably is accomplished in a shorter time atelevated temperatures. The temperature chosen will be regulated by thethermal stability of the explosive-containing mixture which is beingcured, and, of course, curing temperatures are less than the thermaldecomposition temperature of the cap-sensitive explosive. Thus, forexample, a temperature of 200-225 F. is convenient for curingPETN-containing compositions. A further advantage associated with use ofsaid elastomers in the products and process of the present invention isthat the commonly used sulfur and sulfurbearing accelerators are notrequired to cure the initially plastic rubbery mixture. Sulfur andsulfur-bearing vulcanization accelerators are incompatible with manycapsensitive explosives, i.e., degradative chemical reactions may takeplace at elevated temperatures of processing and storage. Thus, theadvantages of good cure at relatively low temperatures, freedom from therequirement of milling which is standard practice with conventionalcurable elastomeric materials, and elimination of sulfur andsulfur-bearing curing agents are highly desirable for highexplosives-containing compositions, as in the present invention, and arecharacteristic of elastomers employed in the practice of this invention.

It will be understood that small amounts of other ingredients, ifdesired, may be incorporated in the explosive compositions of thisinvention; for example, stabilizers, pigments and coloring agents foridentification or for increasing visibility, odorants to create apleasant aroma or overcome an objectionable odor of the curedelastomeric binder matrix, antioxidants and retardants.

Useful shaped articles may be formed from the explosive compositions ofthis invention as hereinbefore described, without incorporatingreinforcing means, and the scope of the invention should be understoodto include such articles. For example, the explosive compositions in anuncured or partially cured state may be shaped into blocks, slabs,tubes, sheets, cords, strips or trains and other forms and finish-curedat room or elevated temperatures. Such explosive articles areelastically extensible and find many uses in the explosive field, buttheir utility is greatly increased by including in the article areinforcing means bound to the explosive composition in such manner asto provide an article having great flexibility, even at subzerotemperatures, little extensibility, and much greater tensile strengththan in the absence of such reinforcing means.

The compositions and articles of the present invention, whether theyinclude a reinforcing means 01" not, are particularly effective and havea high order of utility in the explosives industry because saidexplosive compositions and articles made therefrom are surprisinglyinsensitive to impact and mechanical abuse, they remain completelyeffective after long exposure to water, they require no supplementaryprotective covering for handling, they are nontoxic to users, and incomparison with other explosive compositions used in the industry theyhave enhanced initiating or priming power because of the highconcentration of explosive at the initiation point and the freedom frominert layers of protective covering between initiator and receptorbodies.

Any reinforcing element can be used in the detonating fuse but yarns andthreads are preferred. Yarns which are suitable for use as reinforcingmeans in the detonating fuse will be selected in accordance with thestrength and performance requirements of the fuse. Such yarns may bemade of cotton, linen, jute, silk, wool, rayonespecially high tenacityrayon, cellulose esters, nylon, poly(ethylene terephthalate),polyacrylonitrile, glass or other fibers. Spun fiber yarn constructionusually is preferred to simple monofilament threads since a better bondis established between the spun yarn and the explosive composition ofthe invention. Especially preferred reinforcing means are textured andmultiplex yarns more specifically described below. It is believed thatthe strength of the bond between the explosive composition and thereinforcing means represents a combination of adhesive and mechanicalinterlocking forces.

Completely satisfactory bond strength is attained when the tensilestrength of the article equals or exceeds the tensile strength of thereinforcing means. That is, a sleeve of the explosive composition in thearticles of the present invention will not strip free of the reinforcingmeans when tension is applied between a portion, for example 12 inches,of the article and exposed extensions of the reinforcing means. Yarnswhich are especially suitable as reinforcing means in the fuse, forexample, a column of said explosive composition containing a centralyarn strand or a multiplicity of yarn strands as the reinforcing means,are textured yarns as described in US. Patent No. 2,783,609 andmultiplex yarns as disclosed in copending and coassigned patentapplication of Field, Ser. No. 397,139, filed Sept. 17, 1964. Texturedand multiplex yarns are preferred for use as reinforcing means becauseof the high inherent tensile strength of said yarns and the firm bondwhich is produced between the yarn and the surrounding sheath ofcap-sensitive high explosive composition.

Textured yarn is defined as a bulky yarn comprising a plurality ofsubstantially continuous filaments which are individually convolutedinto coils, loops, and whorls at random intervals along their lengths,and characterized by the presence of ring-like loops irregularly spacedalong the yarn surface.

A multiplex yarn is defined as a wrapped yarn comprising a core composedof at least two continuous integral core elements of textile fibers andsurface wrappings composed of discontinuous textile fibers, the surfacefibers being tightly twisted about the core with portions of fiberslocked into place in the core, and the core fibers being relativelystraight and held together as a compact bundle by the surface wrappings.A multiplex yarn in which the continuous core elements are nylon isespecially preferred for use as the reinforcing means in articles of thepresent invention. The gross tensile strength of said multiplex yarn isconveyed to the shaped articles of this invention because of thestrength of binding which is established between said strand ofmultiplex yarn and the surrounding detonating explosive compositiondescribed herein. For example, use of an 8-ply, 840 denier-per-ply,multiplex nylon yarn as the reinforcing means will result in adetonating fuse having a total diameter of about 0.20 inch and a grosstensile strength in excess of 100 pounds.

For shaped explosive articles in the form of sheets, individual fibersmay be dispersed in the plastic rubbery explosive mixture beforesheeting out, as by calendering, and curing, or yarns may extendlinearly parallel to the long dimension of the sheet. As an alternate,the sheeted explosive composition may be caleudered onto one or bothsides of a latex-impregnated woven fabric or mesh and cured, said wovenfabric or mesh constituting the reinforcing means. Another alternatepermits wrapping reinforcing yarns or threads around an extruded cord ofsaid explosive composition, preferably the surface of said cord iscoated with the aforementioned latex or liquid urethane polymers, andcuring the shaped article. The thread or yarn wrap may be applied as abraided structure over extruded explosive cord which has been precoatedwtih the aforementioned latex or liquid urethane polymer, and the Wholeassembly cured by mild heating. Said woven, wrapped, or braidedstructure in itself provides the necessary tensile strength for thearticle, but the bonding of external reinforcing member to explosivecore is desirable to prevent the covering from unraveling when thearticle, a detonating fuse for example, is cut and to prevent the corefrom slipping out of the external reinforcing means if tension isapplied separately to core and cover. Obviously these methods ofapplying the reinforcing means to the exterior of the shaped explosivecomposition are much more expensive than the aforementioned high speedextrusion of explosive composition about a central reinforcing member ora group of spaced internal reinforcing member. Hence, the use ofinternally placed reinforcing means is preferred in articles of thepresent invention.

Although threads and yarns are preferred as reinforcing means, wire,especially galvanized Wire, may be used for this purpose. It is knownthat the aforementioned elastomeric carboxylic copolymers are stronglyadherent to metal and that they can be cured by reaction with freemetals, especially metals which provide a polyvalent ion. Prominentamong these is zinc. Thus, if some free car boxyl groups are availablein the copolymer-bound explosive composition, or the galvanized wire isprecoated with said carboxylic elastomer before being covered by saidexplosive composition, said composition simultaneously cures and adheresto the galvanized iron wire reinforcing member by reaction betweenthe'zinc coating on said wire and carboxyl groups of said carboxylicelastomer. On the other hand, urethane polymers are good adhesivesbetween wire and explosive composition even in the absence of specificsalt-like chemical bonds.

In one effective embodiment of the present invention, the reinforcingmeans is impregnated with a carboxylic elastomer, for example a latex ofthe kind used in making the explosive composition, or a liquid polyetherurethane such as, for instance, Adiprene L-100. Optionally, theelastomer with which yarns, for example, are impregnated may containplasticizer and curing agents. These promote adhesion between saidreinforcing means and the surrounding composition. A firm bond then isestablished between the reinforcing means and the explosive compositionwith which it is in contact during the curing period which follows theforming or shaping of said articles.

Whatever construction is employed in making articles of this invention,e.g., detonating fuse, the final step in their manufacture is that ofcuring the elastomeric binder matrix and simultaneously binding theexplosive composition to the reinforcing means. Although curing at roomtemperature is known, effective cure can be achieved in shorter times byraising the temperature of the article. Curing at elevated temperaturesis preferred because much less time is required and because abrasionresistance, toughness, and adhesion to the reinforcing means are allincreased. The upper temperature limit for processing, and therebysimultaneously curing the carboxylic copolymer, generally is determinedby the thermal stability of the cap-sensitive explosive ingredient inthe explosive mixture and thus curing temperatures do not exceed thetemperature at which decomposition of the explosive occurs. For example,temperatures of 160-250 F. for 8 to 24 hours are preferred for curingarticles containing PETN, but higher temperatures for shorter times, forexample 8 minutes at 300 F., may be employed with explosives of greaterthermal stability.

The following examples are intended to illustrate the invention further,but not to limit it in any way. Parts and percentages are by weight,unless otherwise specified.

Example 1 parts of ZnO. The order of adding the ingredients is notcritical; however, addition of the particulate high explosive last ispreferred as a somewhat safer procedure. The cover is placed in positionon the mixer, Water at about 160 F. is circulated through the mixerjacket, and the agitator is put in motion. After the mixer has operatedfor about 5 minutes, vacuum gradually is applied, with the agitator inmotion, until a vacuum of about 29 inches or more of mercury isachieved, and this is maintained until substantially all water isremoved from the charge in the mixer. The use of vacuum is not necessaryto com plete removal of water or solvent, but its use is preferredbecause it speeds up processing of the composition. The dried explosivecomposition is transferred from the mixer to the barrel or charginghopper of a ram-type or screwtype extruder fitted with a cross-headtype, circular-orifice die which permits extrusion of the plasticrubbery explosive composition around a multiplex nylon yarn having agross tensile strength of about pounds as it is drawn through the die.The barrel and die-head of the extruder are held at from about to F.while said composition is being extruded. The multiplex nylon yarn maycontain, for example, 8 ends, each of 840 denier, as hereinbeforedescribed, and be preimpregnated with a carboxylic elastomer. The shapedarticle thereby produced is a partially cured detonating fuse having acentral reinforcing means surrounded by a cap-sensitive detonatingcomposition. The detonating fuse as it is continuously extruded may betaken up on a reel, spool, or other storage means. The partially curedfuse is stored at a temperature of from about 200 to 225 F. for about 8hours when the cure is substantially complete. The fuse has a diameterof about 0.180 inch, is totally unaffected by exposure to water, has agross tensile strength of about 125 pounds, is easily primed by acommercial blasting cap, and detonates at a velocity of about 6568meters/sec. (m./s.). The end of a length of primed detonating fuse wasattached to and initiated a block of pressed TNT. The flexibility ofsaid detonating fuse was demonstrated by holding the fuse at -50 F. forabout one hour and then wrapping said cord around a A in. diametermandrel without fracturing or cracking the detonating cord. Thereinforcing yarn is not stripped from the surrounding detonatingcom-position, even under tension up to rupture, nor does the yarn cutthrough the explosive composition.

ll Examples 2 to 6 The table below illustrates additional compositionsprepared according to the procedure of Example 1. The percentagesrepresent the composition on a dry basis, as charged to the mixer.

I claim:

1. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of a cap-sensitive particulatehigh explosive, from about 1 to 20 percent by weight plasticizer, andfrom about Example 2 3 4 5 6 Explosive PETN PETN PETN Tetryl RDX.

Explosive, percent 55 55 55 80 75.

Carboxylic Copolymer Hycar 1572 Hycar 1572 Hy1531572 and Hycar 1572Hycar 1572.

copolymer, percent.-. 33. 36 25 and 8 15. 20.

Plasticizer Dibutylphthalate Flexol 3G0 Flexol 3G0 Flexol 3G0 Flexl sooPlasticizer,percent 8" 7 8 4.25 4.5.

During A nt Detonation Vel., 1n./s

Tensile Strength, lb 1 Low Temp. Flexibility A in. mandrel) 2 1 Flexol3GOtriethyleneglycol di-Z-ethylhexoate made by Union Carbide ChemicalsCo.

1 Reinforcing member was 8 ply, 840 denier/ply multiplex nylon yarn.

3 Lower flex temperatures are obtained for detonating cords if a largerdiameter mandrel is used in the test.

Example 7 An explosive composition is prepared as in Example 1 andextruded without a central reinforcing means. The extruded fuse aftercuring has a diameter of about 0.19 inch and has similar properties tothe cord of Example 1 except that it is elastically extensible at roomtemperature and has a gross tensile strength at 68 F. of about pounds atrupture. The unreinforced fuse of this example is flexible at 50 F. whentested as in Example 1.

Example 8 Parts Superfine PETN 5 8 Hycar 1572 (50% solids) 48.6Triethylene glycol di-Z-ethylhexoate 8.0 ZnO 5.0 Antioxidant (AgeriteWhite) 0.5 Liquid urethane polymers, (polyurethane) 3.0 Adiprene Ll001.0 Adiprene L-315 2.0

Methylene-bis(o-chloroaniline) (MOCA) dissolved in about 7 parts oftrichloroethylene 0.7 Dyestuff 0.5

Extrusion and curing of the mixed explosive composition in the form ofdetonating fuse of circular cross section and having a nylon yarnreinforcing element are carried out as described in Example 1.

Following the teachings of the invention, a novel explosive compositionis obtained that is flexible and exhibits excellent tensile strengthover a wide temperature range of the order of -50 F. to 180 F.Furthermore, the explosive composition can be formed into a variety ofshapes which retain their dimensions under conditions of use; forexample, flexible, extensible detonating fuse may be made, with orwithout a reinforcing means, that is insensitive to impact and effectiveafter exposure to Water for an extended period. In addition, thereinforcing means of the detonating fuse remains integrally bound to theexplosive composition to prevent any detrimental slippage between saidexplosive and reinforcing means under diiferential stress up to therupture stress of the reinforcing means.

15 to 50 percent by weight of a polymeric metallocarboxylate elastomerwhich is the reaction product of a polyvalent metal ion with a copolymerof a butadiene, an acrylic nitrile and an acrylic acid.

2. An explosive composition comprising an intimate uniform mixture offrom about 40 to percent by weight of a cap-sensitive particulate highexplosive, from about 1 to 20 percent by weight plasticizer, from about15 to 50 percent by weight of a polymeric 'metallocarboxylate elastomerwhich is the reaction product of a polyvalent metal ion with a copolymerof a butadiene, an acrylic nitrile and an acrylic acid, and up to 25percent by weight of a polyurethane elastomer.

3. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of a cap-sensitive particulatehigh explosive, from about 1 to 20 percent by weight of a plasticizer,from about 15 to 50 percent by weight of a polymeric metallocarboxylateelastomer which is the reaction product of a polyvalent metal ion with acopolymer of a butadiene, an acrylic nitrile and an acrylic acid, and upto 25 weight percent by weight of a polyurethane elastomer with theproviso that the amount of said urethane does not exceed the amount ofsaid metallocarboxylate elastomer.

4. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of a cap-sensitive particulatehigh explosive; from about 15 to 50 percent by weight of a polymericmetallccarboxylate elastomer which is the reaction product of apolyvalent metal ion with a copolymer of from about 50 to 80 percent byweight of a butadiene, from about 10 to 45 percent by weight of anacrylic nitrile and a sufficient amount of an acrylic acid to providefrom about 0.001 to 0.3 carboxyl equivalents per parts of saidcopolymer, said polyvalent metal ion being present in an amountchemically equivalent to about 0.5 to 2 times the carboxyl content ofsaid copolymer; and from about 1 to 20 percent by weight plasticizer.

5. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of a cap-sensitive particulatehigh explosive; from about 15 to 50 percent by Weight of a polymericmetallooarboxylate elastomer which is the reaction product of apolyvalent metal ion with a copolymer of from about 50 to 80 percent byweight of a butadiene, from about 10 to 45 percent by weight of anacrylic nitrile and a sufficient amount of an acrylic acid to providefrom about 0.001 to 0.3 carboxyl equivalents per 100 parts of saidcopolymer, said polyvalent metal ion being present in an amountchemically equivalent to about 0.5 to 2 times the carboxyl content ofsaid copolymer; from about 1 to 20 percent by Weight plasticizer; and upto about 25 percent by weight of a polyurethane elastomer.

6. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of a cap-sensitive particulatehigh explosive; from about 15 to 50 percent by weight of a polymericmetallocarboxylate elastomer which is the reaction product of apolyvalent metal ion with a copolymer of from about 50 to 80 percent byweight of a butadiene, from about to 45 percent by weight of an acrylicnitrile and a suflicient amount of an acrylic acid to provide from about0.001 to 0.3 carboxyl equivalents per 100 parts by Weight of saidcopolymer, said polyvalent ion being present in an amount chemicallyequivalent to about 0.5 to 2 times the carboxyl content of saidcopolymer from 1 to 20' percent by weight plasticizer; and up to about25 percent by weight of a polyurethane elastomer with the proviso thatthe amount of said urethane does not exceed the amount of saidmetallocarboxylate elastomer.

7. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of a cap-sensitive particulatehigh explosive; from about to 50 percent by weight of a polymericmetallocarboxylate elastomer which is the reaction product of apolyvalent metal ion with a copolymer of from about 50 to 80 percent byweight of butadiene, from about 10 to 45 percent by weight ofacrylonitrile and a sufiicient amount of methacrylic acid to providefrom about 0.001 to 0.3

carboxyl equivalents per 100 parts of said copolymer, said polyvalentmetal ion being present in an amount chemically equivalent to about 0.5to 2 times the carboxyl content of said copolymer; from about 1 topercent by weight plasticizer; and up to about percent by weight of apolyurethane elastomer.

8. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of the cap-sensitive particulatehigh explosive pentaerythritol tetnanitrate; from about 15 to 50 percentby weight of a polymeric metallocarboxylate elastomer which is thereaction product of a polyvalent metal ion with a copolymer of fromabout 50 to 80 percent by weight of butadicue, from about 10 to 45percent by weight of acrylonitrile and a sufiicient amount ofmethacrylic acid to provide from about 0.001 to 0.3 carboxyl equivalentsper 100 parts of said copolymer, said polyvalent metal ion being presentin an amount chemically equivalent to about 0.5 to 2 times the carboxylcontent of said copolymer; from about 1 to 20 percent by weightplasticizer; and up to about 25 percent by weight of a polyurethaneelastomer with the proviso that the amount of said urethane does notexceed the amount of said metallocarboxylate elastomer.

9. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of the cap-sensitive particulatehigh explosive cyclotrimethylenetrinitramine; from about 15 to 50percent by weight of a polymeric metallocarboxylate elastomer which isthe reaction product of a polyvalent metal ion with a copolymer of fromabout 50 to 80 percent by weight of butadiene, from about 10 to 45percent by weight of acrylonitr-ile and a sufi'icient amount ofmethacrylic acid to provide from about 0.001 to 0.3 carboxyl equivalentsper 100 parts of said copolymer, said polyvalent metal ion being presentin an amount chemically equivalent to about 0.5 to 2 times the carboxylcontent of said copolymer; from about 1 to 20 percent by weightplasticizer; and up to about 25 percent by weight of polyurethaneelastomer with the proviso that the amount of said urethane does notexceed the amount of said metallocarboxylate elastomer. 1

10. An explosive composition comprising an intimate uniform mixture offrom about 40 to 80 percent by weight of the cap-sensitive particulatehigh explosive trinitrophenyl methylnitramine; from about 15 to 50percent by weight of a polymeric metallocarboxylate elastomer which isthe reaction product of a polyvalent metal ion with a copolymer of fromabout 50 to 80 percent by weight of butadiene, from about 10 to 45percent by weight of acrylonitrile and a sufiicient amount ofmethacrylic acid to provide from about 0.001 to 0.3 carboxyl equivalentsper 100 parts of said copolymer, said polyvalent metal ion being presentin an amount chemically equivalent to about 0.5 to 2 times the carboxylcontent of said copolymer; from about 1 to 20 percent by weightplasticizer; and up to about 25 percent :by weight of polyurethaneelastomer with the proviso that the amount of said urethane does notexceed the amount of said metallocarboxylate elastomer.

11. An explosive composition comprising an intimate uniform mixture offrom about 40 to percent by weight of the cap-sensitive particulate highexplosive pentaerythritol tetranitrate; from about 15 to 50 percent byweight of a polymeric metallocarboxylate elastomer which is the reactionproduct of the polyvalent metal ion zinc with a copolymer of from about50 to 80 percent by weight butadiene, from about 10 to 45 percent byweight acrylonitrile and sufiicient methacrylic acid to provide fromabout 0.001 to 0.3 carboxyl equivalents per parts of said copolymer,said zinc ions being present in an amount chemically equivalent to about0.5 to 2 times the carboxyl content of said copolymer; from about 1 to20 percent by weight plasticizer; and up to 25 percent by weight of apolyether urethane elastomer with the proviso that the amount of saidurethane does not exceed the amount of said metallocarboxylateelastomer.

12. An explosive composition comprising an intimate uniform mixture ofthe cap-sensitive particulate high eX- plosive pentaerythritoltetranitrate; from about 15 to 50 percent by weight of a polymericmetallocarboxylate elastomer which is the reaction product of thepolyvalent metal ion zinc with a copolymer of from about 50 to 80percent by weight butadiene, from about 10 to 45 percent by weightacrylonitrile and sufiicient methacrylic acid to provide from about 0.02to 0.15 carboxyl equivalents per 100 parts of said copolymer, said zincions being present in an amount chemically equivalent to about 0.5 to 2times the carboxyl content of said copolymer; from about 1 to 20 percentby weight of the plasticizer triethyleneglycol di-Z-ethylhexoate; and upto 25 percent by weight of a polyether urethane elastomer with theproviso that the amount of said urethane does not exceed the amount ofsaid metallocarboxylate elastomer.

13. A process for manufacturing an explosive composition which comprisesintimately mixing a copolymer which is the reaction product of fromabout 50 to 80 percent by weight of a butadiene, from about 10 to 45percent by weight of an acrylic nitrile and a sufiicient amount of anacrylic acid to provide from about 0.001 to 0.3 carboxyl equivalents per100 parts by weight of said copolymer; a source of polyvalent metal ionsin an amount chemically equivalent to about 0.5 to 2 times the carboxylcontent of the copolymer; from about 1 to 20 percent by weight of aplasticizer; from about 40 to 80 percent by weight of a particulatecap-sensitive high explosive; and drying and curing the explosivecomposition.

14. A process for manufacturing an explosive composition which comprisesintimately mixing a dispersion of a copolymer which is the reactionproduct of from about 50 to 80 percent by weight of a butadiene, fromabout 10 to 45 percent by weight of an acrylic nitrile and a suflicientamount of an acrylic acid to provide from about 0.001 to 0.3 carboxylequivalents per 100 parts by weight of said copolymer; a source ofpolyvalent metal ions in an amount chemically equivalent to about 0.5 to2 times the carboxyl content of the copolymer; from 1 to 20 percent byweight of a plasticizer; from about 40 to 80 percent by weight of aparticulate cap-sensitive high explosive; up to about 25 percent byweight of a polyurethane elastomer; and drying and curing the explosivecomposition.

15. A process for the manufacture of an explosive composition whichcomprises intimately mixing an aqueous dispersion of a copolymer whichis the reaction product of from about 50 to 80 percent by weight of abutadiene, from about to 45 percent by weight of an acrylic nitrile anda sufficient amount of an acrylic acid to provide from about 0.001 to0.3 carboxyl equivalents per 100 parts of said copolymer; a source ofpolyvalent metal ions in an amount chemically equivalent to about 0.5 to2 times the carboxyl content of said copolymer; 1 to 20 percent byweight of a plasticizer; 40 to 80 percent by weight of a cap-sensitiveparticulate high explosive; up to about 25 percent by weight of apolyurethane elastomer; removing substantially all the water from themixture, and curing the explosive composition.

16. The process of claim wherein the cap-sensitive high explosive iscyclotrimethylenetrinitramine.

17. The process of claim 15 wherein the capsensitive high explosive istrinitrophenyl methylnitramine.

18. The process of claim 15 wherein the cap-sensitive high explosive ispentaerythritol tetranitrate.

19. A process for the manufacture of an explosive composition whichcomprises intimately mixing an aqueous dispersion of a copolymer whichis the reaction product of from about 50 to 80 percent by weightbutadiene, from about 10 to 45 percent by weight acrylonitrile and asuflicient amount of methacrylic acid to provide from about 0.001 to 0.3carboxyl equivalents per 100 parts of said copolymer; a source of zincions in an amount chemically equivalent to about 0.5 to 2 times thecarboxyl content of the copolymer; from about 1 to percent by weight ofa plasticizer; from about 40 to 80 percent by weight of a cap-sensitiveparticulate high explosive; up to about percent by weight of a polyetherurethane elastomer with the proviso that the amount of said urethanedoes not exceed the amount of copolymer; re-

moving substantially all the water from the mixture, and curing theexplosive composition.

20. The process of claim 19 wherein the cap-sensitive high explosive ispentaerythritol tetranitrate.

21. A process for the manufacture of an explosive composition whichcomprises intimately mixing an aqueous dispersion of a copolymer whichis the reaction product of from about to percent by weight of butadiene,from about 10 to 45 percent by weight of acrylonitrile and a sufficientamount of methacrylic acid to provide from about 0.02 to 0.15 carboxylequivalents per parts of said copolymer; a source of zinc ions in anamount chemically equivalent to about 0.5 to 2 times the carboxylcontent of said copolymer; 1 to 20 percent by Weight of a plasticizer;from about 40 to 80 percent by weight of the particulate cap-sensitivehigh explosive pentaerythritol tetranitrate; up to about 25 percent byweight of polyether urethane elastomer with the proviso that the amountof said urethane does not exceed the amount of said copolymer; removingsubstantially all the water from the mixture, and curing the explosivecomposition.

References Cited UNITED STATES PATENTS 2,999,743 9/1961 Breza et a1.14992 3,102,833 9/1963 Schulz 14919 3,227,588 l/1966 Jones et al. 149183,296,041 1/1967 Wright 1492 3,269,880 8/1966 Visnoz et al. 1492BENJAMIN R. PADGETT, Primary Examiner.

4. AN EXPLOSIVE COMPOSITION COMPRISING AN INTIMATE UNIFORM MIXTURE OFFROM ABOUT 40 TO 80 PERCENT BY WEIGHT OF A CAP-SENSITIVE PARTICULATEHIGH EXPLOSIVE; FROM ABOUT 15 TO 50 PERCENT BY WEIGHT OF A POLYMERICMETALLOCARBOXYLATE ELASTOMER WHICH IS THE REACTION PRODUCT POLYVLENTMETAL ION WITH A COPOLYMER OF FROM ABOUT 50 TO 80 PERCENT BY WEIGHT OF ABUTADIENE, FROM ABOUT 10 TO 45 PERCENT BY WEIGHT OF AN ACRYLIC NITRILEAND A SUFFICIENT AMOUNT OF AN ACRYLIC ACID TO PROVIDE FROM ABOUT 0.001TO 0.3 CARBOXYL EQUIVALENTS PER 100 PARTS OF SAID COPOLYMER, SAIDPOLYVALENT METAL ION BEING PRESENT IN AN AMOUNT CHEMICALLY EQUIVALENT TOABOUT 0.5 TO 2 TIMES THE CARBOXYL CONTENT OF SAID COPOLYMER; AND FROMABOUT 1 TO 20 PERCENT BY WEIGHT PLASTICIZER.